My Science School

 

          Ancient scientists and astronomers were fascinated by moonlight. The ancient Greek philosopher Anaxagoras was one of the first scholars to understand the nature of moonlight. His investigations suggested that the Sun and the Moon were both giant spherical rocks, and that the Moon reflected the light of the Sun.

          The Chinese of the Han dynasty believed in the ‘radiating influence’ of the Moon. They recognized that the light of the Moon was merely a reflection of the Sun. Jing Fang of the Han dynasty studied further about the spherical nature of the Moon.

          Indian astronomer Aryabhatta studied about the physical characteristics of the Moon. In Aryabhatiya, he notes that reflected sunlight is the cause of the shining of the Moon. The Arab astronomer Alhazen threw more light on the way the Moon reflected sunlight. He found that sunlight was not merely reflected from the Moon like a mirror, rather it was emitted from every part of the Moon’s sunlit surface in all directions.

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           The journey to the Moon had to be somehow made possible. This thought was the driving force behind all the studies about the Moon.

           The early developments were crucial in moulding the later growth. It all began thousands of years ago with sketching the Moon; humans began drawing pictures to track the changes of the Moon. Later, their observations of the Moon led to creating calendars.

           Understanding the Moon’s cycles was the earliest development in astronomy. Astronomers from India studied the monthly elongation of the Moon while the Babylonian astronomers worked towards finding formulas to predict the lunar eclipse. The Chinese astronomer Shi Shen is noted for his instructions for predicting solar and lunar eclipses. The Chinese also studied the physical form of the Moon, including moonlight and gravitational pull. There were also efforts to calculate the distance between the Earth and the Moon. However, the Moon was believed to be a sphere with a smooth surface before the invention of the telescope.

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          We are familiar with the word lunacy, which means madness. Did you know that this word comes from Luna, the Latin word for the Moon?

          There are many stories about mysterious events that happen during the full moon. This includes strange and violent behaviour of animals including wolves and dogs. It is believed that the full moon brings out the worst in humans and animals. However, there are no satisfactory scientific explanations for any of this, though there are some evidences about the lunar phases affecting the behaviour of birds, fish, insects and even mammals. It’s a growing research area now.

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          About 350 million years ago, a day on the Earth was around three hours shorter than today. The Earth slowed down because of the Moon. Aren’t you surprised?

          The Moon can slow down the Earth, even with its weak gravitational and magnetic field. This happens when there’s a force of friction between the surface of the Earth and the tidal bulges.

          During its rotation, the Earth drags the tidal bulge directly under the Moon. This causes friction between the Earth’s surface and the tidal bulge. The friction generated during this action slows down the rotation of the Earth on its axis. This results in a longer day and even a longer month.

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          The oceans and seas rise and fall at definite intervals. This rise and fall happens because of the gravitational force between the Earth and the Moon.

          We know that the Moon has a weak gravitational force. But it is strong enough to cause these periodic rises and falls known as tides.

          As our planet rotates, the Moon’s pull is exerted on different parts of the Earth. The Moon’s gravitational force exerts a pull on the oceans that generates tidal energy. It causes both the Earth and the oceans to bulge out in the direction of the Moon and away from it, and is known as tides. Because of the rotation of the Earth around the Sun, two tides occur each day- high tide and low tide.

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          Will a month have two full moons? Sounds almost impossible. Let’s take a look. The Moon takes almost twenty nine and a half days to change from one full moon to another. But, an average month has a span of thirty days. This makes it very unlikely for a month to have two full moons.

          However, some months do have two full moons and it happens very rarely. If there are two full moons in a month, the second full moon is called ‘blue moon.’ This name is not linked to the colour. In a century, there will be forty-one blue moons.

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          For a while, we have been talking about sunlight illuminating the Moon. What would happen if something blocks the sunlight that it receives? Will the Moon vanish from the night sky?

          In some instances, the Earth blocks the sunlight that is supposed to fall on the surface of the Moon. This happens when the Earth’s shadow falls on the Moon as it comes between the Sun and the Moon. This phenomenon is known as lunar eclipse.

          Lunar eclipse happens only during the full moon when the Earth either blocks sunlight completely or partially. Depending on this, lunar eclipse can be total or partial. However, the Moon will not disappear completely during the eclipse. This is because of a small amount of indirect sunlight that falls on it.

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          It takes almost 27 days for the Moon to complete one trip around the Earth. This is known as the sidereal month. But it takes almost 29 days to change from a new moon to the next new moon. This is known as the synodic month. There is a difference of roughly two days. Wonder why?

          We already know that the Moon’s phases change according to the sunlight that falls on it and new moon occurs when the Moon is placed between the Earth and the Sun.

          While the Moon moves around it, the Earth moves around the Sun. The Earth moves farther in space during the time the Moon completes one orbit. So, for the Moon to come between the Earth and the Sun again, it has to move a little farther. It takes two days for the Moon to travel this extra distance.

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          The shape of the Moon changes throughout the lunar month. The period in which the new moon grows to a full moon and back to another new moon is known as a lunar month.

          A lunar month is characterized by waxing and waning. Waxing occurs between the new moon and full moon, when the moon grows in size. The side of the Moon illuminated by the sunlight becomes bigger; it grows from a waxing crescent to waxing gibbous and then to full moon. During the gibbous phase, 51-99 per cent of the moon’s surface is illuminated.

          On the other hand, waning occurs between the full moon and new moon. When the Moon is waning, its surface illuminated by the sunlight decreases day-by-day. The Moon changes from full moon to the waning gibbous phase. It then changes to the waning crescent and finally the new moon.

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          When the Moon and Sun are placed at opposite directions from the Earth, the sunlight falls on the side facing the Earth. Therefore, the Moon appears as a round shining disc and is known as full moon.

          On the other hand, when the Moon comes between the Earth and the Sun, sunlight falls on the side that faces away from the Earth. During this time, the side facing the Earth appears dark and is known as new moon. The sky looks bright during the full moon while the Moon will not be visible during the new moon, making it dull.

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          The Moon does not appear in the same shape every day, it is ever changing. On some days, it looks like a shining disk, on some days it looks like an elongated C. These different shapes of the Moon are called the phases of the Moon.

          The orbiting of the Moon around the Earth is the secret behind the different phases of the Moon. We already know that the Moon has no light of its own. As the Moon moves around the Earth, different parts of it are lit by the Sun, thus causing different phases. In a fortnight’s time, the Moon goes from full moon to new moon.

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          The Apollo astronauts placed instruments known as seismographs on the Moon to study about its interior. What we know about it now comes primarily from their studies.

          The Moon is made up of different layers like any other celestial body. It has an outer crust, an inner mantle and an innermost core. The outer crust is hard, dry and dusty. It is almost 60 kilometres thick in the near side while it is almost twice as thick in the far side.

          The mantle has a thick layer of rock at the exterior and is semi-rigid in the interior. The mantle runs down almost 800 kilometres. The Moon’s core is constituted of rocks rich in iron.

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          Scientists have special terms to indicate each scientifically relevant object around us. At times, these words may confuse an ordinary person as scientists often use big words that are difficult for a common man to understand. For instance, the scientific term for dry skin is xerosis. Similarly, lunar soil is known as lunar regolith among scientists.

          Lunar regolith is formed as a result of comets or meteorites that fall on the surface of the Moon. It is rich in oxygen and various metals. The thickness of the regolith varies from one place to another; it is three to five metres thick in the Maria, while the thickness in the highlands is ten to twenty metres.

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          The temperature on the Moon is not constant; it varies from boiling hot to freezing cold, depending on the position of the Sun. The Moon has no atmosphere to either trap the heat or to insulate its surface.

          A day on Earth is 24 hours. Daytime on the Moon is thirteen and a half Earth days long. A long night of thirteen and a half days follows a Moon’s day. When sunlight hits the surface of the Moon during the day, the temperature can go up to 127 degree celsius. In contrast, the temperature on the Moon can drop to minus 173 degree celsius during the night.

          The temperature at the Moon’s core is much higher than its surface temperature. However, there are regions on the Moon that never receive sunlight. This is because of the slight tilt of its axis. Unlike Earth, the Moon doesn’t have different seasons either.

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          If you take a compass to the Moon, it would not point northwards. It is not because your compass is faulty. A compass shows directions in alignment with the Earth’s magnetic field. We already know that the Moon has a very weak gravitational field. It does not have a strong magnetic field either. To understand this better, let us take a look at how the Earth’s magnetic field is formed.

          The core of the Earth is filled with hot liquid iron. This molten iron swirls as our planet rotates, thus producing the Earth’s magnetic field. The Moon’s core is less dense than the Earth. Therefore, the Moon’s core may contain only a little amount of metal; this might not even be heavy iron. On the Moon, the fluid motion of the conducting material is either very less or not present at all. As a result, the Moon has a weak magnetic field compared to that of Earth. It is around one hundredth of the Earth’s magnetic field.

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